Continuous isobutylene-assisted aqueous extraction of methanol from methyl tertiary butyl ether

ABSTRACT

An impure methyl tertiary butyl ether product contaminated with isobutylene, methanol and water is purified by continuous counter-current contact with water and isobutylene in a counter-current contact extraction tower to provide an overhead extract comprising isobutylene, methyl tertiary butyl ether and water and a raffinate comprising methanol, water and a minor amount of methyl tertiary butyl ether, the overhead raffinate being separated in a methyl tertiary butyl ether purification distillation zone into a lighter distillation fraction comprising isobutylene and water and a heavier distillation fraction consisting essentially of methyl tertiary butyl ether, the lighter distillation fraction being decanted to remove water and to provide a distillate isobutylene fraction that is charged to a surge drum from which isobutylene is returned to the contact tower.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates to the manufacture and isobutylene-assistedpurification of methyl tertiary butyl ether. More particularly, thisinvention relates to a process for the manufacture of methyl tertiarybutyl ether from tertiary butyl alcohol and methanol and to thepurification of a methanol-contaminated methyl tertiary butyl etherintermediate product formed during the process; the intermediate productbeing purified by counter-current contact with water in an extractiontower, wherein isobutylene is added to the extraction tower to assist inthe formation of a raffinate composed of methyl tertiary butyl ether,isobutylene and residual water and an extract comprising methanol,residual isobutylene, residual methyl tertiary butyl alcohol and water.

Still more particularly, this invention relates to a process for themanufacture of methyl tertiary butyl ether from tertiary butyl alcoholand methanol and to the purification of a methanol-contaminated methyltertiary butyl ether intermediate product formed during the process; theintermediate product being purified by counter-current contact withwater in an extraction tower, wherein isobutylene is added to theextraction tower in admixture with the methanol-contaminated methyltertiary butyl ether to assist in the formation of a raffinate composedof methyl tertiary butyl ether, isobutylene and residual water and anextract comprising methanol, residual isobutylene, residual methyltertiary butyl ether and water.

Even more particularly, this invention relates to a method ofpurification of methanol-contaminated methyl tertiary butyl ether bycounter-current contact with water in an extraction tower, whereinisobutylene is separately added to the extraction tower below the pointat which the methanol-contaminated methyl tertiary butyl ether isintroduced in order to selectively strip at least a portion of theresidual methyl tertiary butyl ether from the extract.

2. Prior Art

In U.S. Pat. No. 4,144,138 (1979) to Rao et al., there is disclosed amethod for recovering methyl tertiary butyl ether from etherificationreaction effluent by azeotropic distillation to recover methanol-etherazeotrope overhead which is water-washed to give pure ether raffinate,the latter being azeotropically distilled to yield ether-methanoloverhead which is recycled to water washing.

The preparation of methyl tert-butyl ether from methyl and tert-butylalcohols is discussed in S. V. Rozhkov et al., Prevrashch Uglevodorodov,Kislotno-Osnovn. Geterogennykh Katal. Tezisy Dokl., Vses. Konf., 1977,150 (C. A. 92:58165y). Here the TBA and methanol undergo etherificationover KU-2 strongly acidic sulfopolystyrene cation-exchangers under mildconditions. This reference contains data on basic parameters of such aprocess.

Liquid-liquid extraction is described in an article by Cusak et al., "AFresh Look at Liquid-Liquid Extraction" (Chemical Engineering, March1991, pp. 132-138) and an article by Cusak et al. also entitled "A FreshLook at Liquid-Liquid Extraction" (Chemical Engineering, February 1991,pp. 66-76).

BACKGROUND INFORMATION

Methyl tert-butyl ether is finding increasing use as a blendingcomponent in high octane gasoline as the current gasoline additivesbased on lead and manganese are phased out. Currently all commercialprocesses for the manufacture of methyl tert-butyl ether are based uponthe liquid-phase reaction of isobutylene and methanol catalyzed by acationic ion-exchange resin.

With the expanding use of MTBE as an acceptable gasoline additive, agrowing problem is the availability of raw materials. Historically, thecritical raw material is isobutylene (Oil and Gas J., Jun. 8, 1987, p.55). It would be advantageous, therefore, to have a process to make MTBEthat does not require isobutylene as a building block. It would beadvantageous to have an efficient process for making MTBE by reaction ofmethanol with tertiary butyl alcohol, since t-butanol (TBA) is readilyavailable commercially through isobutane oxidation.

It is known to react methanol with tertiary butyl alcohol in thepresence of a catalyst in order to produce methyl tertiary butyl ether.A wide variety of catalysts have been suggested for this purpose.

In U.S. Pat. No. 2,282,469 to Frolich there is disclosed a process forpreparing methyl tertiary butyl ether over a catalyst comprisingKieselguhr impregnated with phosphoric acid at a temperature of about175° F. to 350° F.

Japanese Patent 0007432 teaches the use of zeolites to make dialkylethers containing primary or secondary alkyl groups. The zeolites have aporous structure and are represented by:

    M.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2..sub.y H.sub.2 O

where M is an alkali metal or alkaline earth metal cation or organicbase cation, n is the valence of the cation and x and y are variables.

U.S. Pat. No. 4,058,576 to Chang et al. teaches the use of(pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a poresize greater than 5 angstrom units and a silica-to-alumina ratio of atleast 12, to convert lower alcohols to a mixture of ethers and olefins.

In U.S. Pat. No. 4,822,921 there is disclosed a method for producingMTBE by reacting tertiary butyl alcohol and methanol in the presence ofa catalyst comprising an inert support, such as titania, having aphosphoric acid impregnated thereon.

U.S. Pat. No. 4,827,048 discloses a method for producing MTBE byreacting tertiary butyl alcohol and methanol in the presence of acatalyst comprising a heteropoly acid such as 12-tungstophosphoric acidor 12-molybdophosphoric acid on an inert support, such as titania.

Two of the principal by-products formed during the reaction of themethanol with the tertiary butyl alcohol are water and isobutylene.Methanol and methyl tertiary butyl ether form an azeotrope which isbroken only with difficulty and therefore the separation of methanolfrom MTBE during the recovery of purified methyl tertiary butyl etherpresents a serious problem.

In U.S. Pat. No. 4,820,877, separation of methanol from MTBE isaccomplished by using a refinery fuel gas to enhance the separation ofmethanol into the overhead stream of a distillation column.

In U.S. Pat. No. 4,814,517, separation of methanol from MTBE isaccomplished by using a silica gel to preferentially adsorb methanolfrom an MTBE stream and by periodically regenerating the silica gel.

In U.S. Pat. No. 4,798,674, separation of methanol from MTBE isaccomplished by using a membrane of cross-linked polyvinyl alcohol or aquaternary ammonium ion resin. Methanol preferentially permeates throughthe membrane increasing the MTBE concentration of the charge liquid.

In U.S. Pat. No. 4,759,850, separation of methanol from MTBE isaccomplished by reverse osmosis.

In U.S. Pat. No. 4,440,963, separation of methanol from MTBE isaccomplished by adding an agent such as 2-methyl pentane or Freon 113 toform an azeotrope with methanol. This azeotrope is recovered overheadgiving a methanol-free MTBE bottoms product.

As recognized by Rao et al. in U.S. Pat. No. 4,144,138, isobutylene isformed as a by-product when methanol is reacted with tertiary butylalcohol. In accordance with the Rao process, the isobutylene isseparated from the reaction product in an initial azeotropicdistillation step as a noncondensable gas. Rao taught that theisobutylene may be flashed from the reaction product for recycle,depending upon purity.

SUMMARY OF THE INVENTION

Isobutylene is produced as a by-product when the methanol-contaminatedmethyl tertiary butyl ether is produced by the reaction of tertiarybutyl alcohol with methanol.

In accordance with the present invention, a process is provided whereinthe isobutylene is utilized downstream of the etherification reactionzone as a reactant, together with methanol, in the preparation ofadditional methyl tertiary butyl ether and wherein, in the purificationof a methanol-contaminated methyl tertiary butyl ether intermediateproduct by counter-current contact with water in an extraction tower,isobutylene is used to facilitate in the removal of residual methyltertiary butyl ether from the extract.

In the continuous practice of the process of the present invention forthe manufacture of methyl tertiary butyl ether and for the continuouspurification of a methanol-contaminated methyl tertiary butyl etherintermediate product with water in an extraction tower, isobutylene isadded to the extraction tower to assist in the purification.

A comparatively large volume of isobutylene recycle is required for usein the extraction tower. However, process upsets can result in atemporary loss of produced methyl tertiary butyl ether and isobutylene.Such an event has the potential for shutting down the entire process,including the isobutylene-assisted water extraction of methanol frommethyl tertiary butyl ether.

In accordance with another embodiment of the present invention, anintermediate isobutylene storage drum, or surge drum, is providedupstream of the water extraction step to eliminate the potential forupsets in the water extraction step due to a shortage of isobutylene,and also to provide isobutylene inventory for start-ups and shut downs.

Also, when tertiary butyl alcohol is prepared from tertiary butylhydroperoxide, the tertiary butyl alcohol reaction product will containminor amounts of peroxide contaminants such as tertiary butylhydroperoxide, ditertiary butyl peroxide, allyl tertiary butyl peroxide,etc. When tertiary butyl alcohol contaminated with minor amounts ofperoxides is reacted with methanol to form methyl tertiary butyl ether,the etherification reaction product resulting from the reaction willcontain the peroxide contaminants.

In accordance with another embodiment of the present invention, aperoxides-contaminated tertiary butyl alcohol feedstock is passedthrough a peroxides decomposition reaction zone before being charged tothe methyl tertiary butyl ether etherification reaction zone so that themethyl tertiary butyl ether etherification product will be substantiallyfree from peroxide contaminants.

In accordance with a further embodiment of the present invention, anintegrated process is provided wherein a peroxides-contaminated tertiarybutyl alcohol feedstock is passed through a peroxides decompositionreaction zone to substantially completely decompose the peroxidecontaminants contained therein, and then charged to a methyl tertiarybutyl ether etherification reaction zone together with methanol to forman isobutylene-containing methyl tertiary butyl ether etherificationproduct that is substantially free from peroxide contaminants, whereinby-product isobutylene is utilized downstream of the etherificationreaction zone as a stripping agent in the purification of the methyltertiary butyl ether and wherein the by-product isobutylene is used as areactant in the preparation of additional methyl tertiary butyl ether.

DESCRIPTION OF PREFERRED EMBODIMENTS I

In accordance with a preferred embodiment of the present invention, amethod for the continuous preparation of methyl tertiary butyl ether(MTBE) from tertiary butyl alcohol (TBA) and methanol (MeOH) is providedcomprising the steps of:

a) continuously charging a peroxides-contaminated tertiary butyl alcoholfeedstock to a peroxides decomposition reaction zone and substantiallycompletely decomposing the peroxide contaminants therein to form asubstantially peroxides-free tertiary butyl alcohol product,

b) continuously charging a reaction feed mixture comprising methanol andthe substantially peroxides-free tertiary butyl alcohol product to anetherification reaction zone containing a bed of a TBA/MeOHetherification catalyst and reacting said reaction feed mixture thereinto form an etherification reaction product comprising unreactedmethanol, unreacted tertiary butyl alcohol, water, isobutylene (IBTE)and methyl tertiary butyl ether,

c) continuously charging the etherification reaction product to a firstmethyl tertiary butyl ether distillation zone and separating it thereininto a first lighter distillation fraction comprising isobutylene,methanol and methyl tertiary butyl ether and a second heavierdistillation fraction comprising methanol, tertiary butyl alcohol andwater,

d) continuously charging an isobutylene reaction mixture comprising thefirst distillation fraction and a first recycle isobutylene (IBTE)fraction to an isobutylene conversion reaction zone containing a solidresin IBTE/MeOH etherification catalyst and partially reacting theisobutylene and methanol contained in the isobutylene reaction mixtureto form an isobutylene conversion product,

e) continuously charging the isobutylene conversion product to amethanol extraction zone comprising a counter-current extraction towerand counter-currently contacting the isobutylene conversion producttherein with water to provide an overhead raffinate comprisingisobutylene, methyl tertiary butyl ether and a minor amount of water anda raffinate comprising methanol, water and minor amounts of methyltertiary butyl ether and isobutylene,

f) continuously charging the raffinate to a second methyl tertiary butylether distillation zone and separating it therein into a third lighterdistillation fraction comprising isobutylene and water and a fourthheavier distillation fraction consisting essentially of methyl tertiarybutyl ether,

g) continuously charging the third distillation fraction to adecantation separation zone and separating it therein into anisobutylene fraction and a water fraction,

h) continuously recycling a first portion of said isobutylene fractionto the isobutylene reaction conversion zone as the first isobutylenerecycle fraction, and

i) continuously recycling a second portion of the isobutylene fractionto the methanol extraction zone as the methyl tertiary butyl etherstripping agent.

II

Another preferred embodiment of the present invention comprises a methodfor the continuous preparation of methyl tertiary butyl ether fromtertiary butyl alcohol (TBA) and methanol (MeOH), including:

b') continuously reacting a mixture of methanol and tertiary butylalcohol in an etherification reaction zone containing a bed of aTBA/MeOH etherification catalyst to form an etherification reactionproduct comprising unreacted methanol, unreacted tertiary butyl alcohol,water, isobutylene (IBTE) and methyl tertiary butyl ether,

c') continuously charging the etherification reaction product to a firstmethyl tertiary butyl ether distillation zone and separating it thereininto a first lighter distillation fraction comprising isobutylene,methanol and methyl tertiary butyl ether and a second heavierdistillation fraction comprising methanol, tertiary butyl alcohol andwater,

d') continuously charging an isobutylene reaction mixture comprising thefirst distillation fraction and a first recycle isobutylene (IBTE)fraction to an isobutylene conversion reaction zone containing a solidresin IBTE/MeOH etherification catalyst and partially reacting theisobutylene and methanol contained in the isobutylene reaction mixtureto form an isobutylene conversion product,

e') continuously charging the isobutylene conversion product to amethanol extraction zone comprising a counter-current contact tower andcounter-currently contacting the isobutylene conversion product withwater to provide an overhead raffinate comprising isobutylene, methyltertiary butyl ether and a minor amount of water and an extract which iscounter-currently stripped with isobutylene to remove residual amountsof methyl tertiary butyl ether.

f') continuously charging the raffinate to a second methyl tertiarybutyl ether distillation zone and separating it therein into a thirdlighter distillation fraction comprising isobutylene and water and afourth heavier distillation fraction consisting essentially of methyltertiary butyl ether,

g') continuously charging the third distillation fraction to adecantation separation zone and separating it therein into anisobutylene fraction and a water fraction,

h') continuously recycling a first portion of the isobutylene fractionto the isobutylene reaction zone as the first isobutylene recyclefraction, and

i') continuously recycling a second portion of said isobutylene fractionto the methanol extraction zone as the methyl tertiary butyl etherstripping fraction.

III

In accordance with a third preferred embodiment of the presentinvention, a method for the continuous preparation of methyl tertiarybutyl ether is provided wherein the second heavier distillation fractionfrom the first methyl tertiary butyl ether distillation zone and theextract from the methanol extraction zone are further processed in orderto recover the methyl tertiary butyl ether contained therein and inorder to obtain the methanol and tertiary butyl alcohol containedtherein for recycle, comprising the steps of:

j) continuously charging the extract from the methanol extraction zoneto a third methyl tertiary butyl ether distillation zone and separatingit therein into a lighter fifth distillation fraction comprising methyltertiary butyl ether and a heavier sixth distillation fractioncomprising water and methanol,

k) continuously charging the sixth distillation fraction to a fourthmethanol distillation zone and separating it therein into a seventhlighter methanol recycle fraction and an eighth heavier distillationfraction,

l) continuously charging the second heavier distillation fraction to afifth distillation zone and separating it therein into a ninth lighterdistillation recycle fraction comprising methanol and tertiary butylalcohol, and a tenth heavier distillation fraction,

m) continuously charging the fifth distillation fraction to the methanolextraction zone, and

n) continuously charging the seventh distillation fraction and the ninthdistillation fractions to the etherification reaction zone.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The Etherification Reaction Catalyst

In accordance with the MTBE manufacture and purification method of thepresent invention, an etherification reaction zone containing a bed ofetherification catalyst is utilized. A wide variety of etherificationcatalysts can be used for this purpose, such as supported phosphorusacid-type catalysts. A preferred catalyst is a sulfonic acid resinetherification catalyst such as a sulfonated polystyrene resincross-linked with divinyl benzene.

Any suitable solid resin etherification catalyst may be used for thispurpose, such as a strongly acidic ion exchange resin consistingessentially of sulfonated polystyrene, such as a divinyl benzenecrosslink polystyrene matrix containing from about 0.5 to about 20% ofcopolymerized divinyl benzene. Resins of this nature are manufacturedand sold commercially under various trade names such as "Dowex 50","Nalcite HCR" and "Amberlyst 15". The use of catalyst of this nature isdisclosed, for example, in Rao U.S. Pat. No. 4,144,138.

Also, Kieselguhr impregnated with phosphoric acid as disclosed inFrolich U.S. Pat. No. 2,282,469, titania having phosphoric acidimpregnated thereon as disclosed in Knifton U.S. Pat. No. 4,822,921, ahetero polyacid such as 12-tungstophosphoric acid or12-molybdophosphoric acid supported on titania, etc., may be used.

Zeolites as disclosed in Japanese Patent 0007432 or aluminosilicatezeolites as disclosed in Chang et al. U.S. Patent No. 4,058,576 may alsobe used.

The reaction conditions to be utilized when reacting methanol withtertiary butyl alcohol in the presence of a sulfonic acid resinetherification catalyst of the type disclosed in the prior art include areaction temperature of about 90° to about 140° C., a pressure of about30 to about 500 psia and a space velocity of about 0.5 to about 20volumes of feed per volume of etherification catalyst per hour.

The Solid Resin Etherification Catalyst

In accordance with the present invention, a distillate fraction obtainedduring the recovery process, identified above as the first distillationfraction, and which contains both isobutylene and methanol is broughtinto contact with a solid resin etherification catalyst, as describedabove, in order to convert a significant portion of the isobutylene andmethanol to methyl tertiary butyl ether.

The first distillation fraction will normally contain from about 5 toabout 10 wt. % of isobutylene, from about 70 to about 80 wt. % of methyltertiary butyl ether and from about 10 to about 20 wt. % of methanol.

An isobutylene reaction mixture is prepared from the first distillationfraction and a first isobutylene recycle fraction so as to provide anisobutylene reaction mixture containing about an additional 1 to 10 wt.% of isobutylene, based on the weight of the first distillationfraction. Thus, the isobutylene reaction mixture may comprise from about6 to about 15 wt. % of isobutylene, from about 65 to about 75 wt. % ofmethyl tertiary butyl ether and from about 10 to about 20 wt. % ofmethanol.

Any suitable solid resin etherification catalyst may be used for thispurpose, such as a strongly acidic ion exchange resin consistingessentially of sulfonated polystyrene, such as a divinyl benzenecrosslink polystyrene matrix containing from about 0.5 to about 20% ofcopolymerized divinyl benzene. Resins of this nature are manufacturedand sold commercially under various trade names such as "Dowex 50","Nalcite HCR" and "Amberlyst 15". The use of catalyst of this nature isdisclosed, for example, in Rao U.S. Pat. No. 4,144,138.

It is contacted with a solid resin etherification catalyst in theisobutylene conversion reaction zone under conversion conditionsincluding, for example, a temperature of about 35° to about 130° C., apressure of about 30 to about 500 psia and a contact time of about 0.5to about 20 volumes of first distillate fraction per volume ofetherification catalyst per hour. As a consequence, an isobutyleneconversion product is formed which will normally contain from about 0 toabout 10 wt. % of isobutylene, about 75 to about 85 wt. % of methyltertiary butyl ether and from about 10 to about 15 wt. % of methanol.

Peroxide Decomposition

When the tertiary butyl alcohol feedstock to be used in the preparationof methyl tertiary butyl ether is tertiary butyl alcohol contaminatedwith peroxides such as tertiary butyl hydroperoxide, ditertiarybutylperoxide, allyl tertiary butyl peroxide, etc., the feedstock is treatedfor the substantially complete removal of the peroxide contaminantsbefore it is charged to the methyl tertiary butyl ether etherificationzone.

It is known to prepare tertiary butyl alcohol by the thermal orcatalytic decomposition of tertiary butyl hydroperoxide. It is alsoknown to prepare tertiary butyl alcohol by the catalytic reaction oftertiary butyl hydroperoxide with propylene to form propylene oxide andtertiary butyl alcohol. The tertiary butyl alcohol feedstock derivedfrom tertiary butyl hydroperoxide in this manner will contain peroxidecontaminants. A typical feedstock prepared in this fashion will containfrom about 95 to 99 wt. % of tertiary butyl alcohol and less than about2.0 wt. % of peroxide contaminants.

In accordance with the present invention, the peroxides contaminatedtertiary butyl alcohol is charged to a peroxides decomposition reactionzone where the peroxides are substantially completely thermally and/orcatalytically decomposed. The peroxide contaminants will be decomposedto form water and tertiary butyl alcohol, and trace amounts of otherdecomposition products such as acetone and methyl formate.

When the peroxides are to be thermally decomposed, theperoxides-contaminated tertiary butyl alcohol feedstock is continuouslypassed through a reactor in the peroxides decomposition reaction zone ata temperature of about 100° to about 200° C., a pressure of about 80 toabout 500 psia at a flow rate of about 0.5 to 20 volumes of feedstockper reactor volume per hour to thereby provide a substantiallyperoxides-free tertiary butyl alcohol reaction product.

Alternately, the peroxide contaminants may be catalytically decomposed.

A wide variety of catalysts may be used for this purpose, such as cobaltborate as disclosed in U.S. Pat. No. 4,547,598, a nickel, copper,chromia catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,704,482, an iron, copper, chromia, cobalt catalyst as disclosed inSanderson et al. U.S. Pat. No. 4,705,903, a base treated hydrogenationcatalyst from groups VIB or VIIIB of the Periodic Table as disclosed inSanderson et al. U.S. Pat. No. 4,742,179, a nickel, copper, chromium andbarium catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,873,380, a metal phthalocyanine catalyst as disclosed in Sanderson etal. U.S. Pat. No. 4,910,349, an imidazole-promoted methyl metalphthalocyanine catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,912,266, a base promoted metal phthalocyanine catalyst as disclosed inSanderson et al. U.S. Pat. No. 4,912,267, a solid ruthenium catalyst asdisclosed in Sanderson et al. U.S. Pat. No. 4,922,033, a promoted metalporphine catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,922,034, etc.

The conversion conditions to be utilized in the peroxide decompositionzone may comprise, for example, a temperature of about 100° to about200° C., a pressure of about 80 to about 500 psia and a space velocityof about 0.5 to about 20 volumes of feed per volume of catalyst perhour.

The effluent from the peroxide decomposition zone will typicallycomprise about 95 to about 99 wt. % of tertiary butyl alcohol and lessthan about 0.1 wt. % of peroxide contaminants.

BRIEF DESCRIPTION OF THE DRAWING

In the drawings:

FIG. 1 is a schematic flow sheet with conventional parts omitted showingthe general reaction and recovery sequence comprising the process of thepresent invention for the manufacture and purification of methyltertiary butyl ether; and

FIG. 2 is a fragmentary schematic flow sheet, with conventional partsomitted, showing part of the general sequence of FIG. 1 and illustratinga preferred method for the purification of a methanol-contaminatedmethyl tertiary butyl ether intermediate product by counter-currentcontact with water in an extraction tower, using isobutylene to stripmost of the residual methyl tertiary butyl ether from the extract.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1, there is shown a schematic flow sheetillustrating the preferred method for the practice of the process of thepresent invention. In the figure, conventional parts, such as valves,pumps, temperature control sensors, pressure sensors, heaters, coolers,flow control regulation apparatus, reflux condensers, reboilers, etc.,have been omitted.

In accordance with the present invention, there is provided anetherification reaction zone 10 containing a bed of solid etherificationcatalyst. Any suitable etherification catalyst may be used such as, forexample, a solid resin etherification catalyst of the type describedabove, such as a strongly acidic ion exchange resin consistingessentially of sulfonated polystyrene crosslinked with divinyl benzene(e.g., Dowex 50, Nalcite HCR, Amberlyst 15, etc.). As another example,the catalyst may be a fluorophosphoric acid-on-titania catalyst of thetype disclosed in Knifton et al. U.S. Pat. No. 4,822,921 or a heteropolyacid such as 12-tungstophosphoric acid or 12-molybdophosphoric acidsupported on an inert support such as titania.

When the tertiary butyl alcohol is prepared by the thermal or catalyticdecomposition of tertiary butyl hydroperoxide, it will contain minoramounts of impurities such that, for example, the feedstock charged tothe reaction zone 10 will contain the following components:

ETHERIFICATION REACTION ZONE FEED MIXTURE

    ______________________________________                                                       wt. %                                                          Component      (approximate)                                                  ______________________________________                                        Methanol       41.0                                                           TBA.sup.1      47.0                                                           Acetone        0.5                                                            2-Propanol     6.0                                                            MTBE.sup.2     0.2                                                            DTBP.sup.3     0.1                                                            t-Butyl Formate                                                                              0.1                                                            Water          6.0                                                                           100.9%                                                         ______________________________________                                         .sup.1 Tertiary butyl alcohol                                                 .sup.2 Methyl tertiary butyl ether                                            .sup.3 Ditertiary butyl peroxide                                         

When the tertiary butyl alcohol feedstock to be initially charged toetherification reaction zone 10 is a peroxides contaminated tertiarybutyl alcohol feedstock, as described above, the tertiary butyl alcoholfeedstock is initially charged by way of a tertiary butyl alcohol feedline 13 to a peroxides decomposition zone 11, such as, for example athermal peroxides decomposition zone 11 operated, (e.g.) at atemperature of about 100° to about 200° C., a pressure of about 80 toabout 500 psia and a flow rate of about 0.5 to 20 volumes of feedstockper reactor volume per hour to thereby provide a substantiallyperoxides-free tertiary butyl alcohol reaction product. The peroxidecontaminants will be decomposed to form water and tertiary butylalcohol, and trace amounts of other decomposition products such asacetone and methyl formate.

The substantially peroxides-free tertiary butyl alcohol reaction productis continuously discharged from the peroxides decomposition zone 11 by adischarge line 17 leading to a manifold 12. Fresh methanol iscontinuously charged to the manifold 12 by a line 15, as is a recyclestream 112 containing recycle methanol and recycle tertiary butylalcohol. The flow of methanol and tertiary butyl alcohol to the manifold12 through the lines 15, 17 and 112 is regulated so that a molar excessof methanol is present in the line 14 leading to the etherificationreaction zone 10, such as, for example, a molar ratio of about 1.1 toabout 3 moles of methanol per mol of tertiary butyl alcohol.

Within the etherification reaction zone 10, the feed mixture is broughtinto contact with a bed of etherification catalyst, such as a sulfonicacid resin etherification catalyst under reaction conditions including apressure of about 30 to about 500 psia, and more preferably from about200 to about 300 psia, a temperature of about 30° to about 200° C., andmore preferably from about 80° to about 140° C., and still morepreferably from about 90° to about 130° C. When the catalyst is asupported phosphorus acid-type catalyst, the reaction temperature maysuitably be in the range of about 150° to about 190° C.

Contact time within the etherification reaction zone is suitably suchthat about 0.5 to about 20 volumes of feed mixture per volume ofetherification catalyst per hour are fed to the etherification reactionzone 10 and, more preferably from about 1 to about 4 volumes of feedmixture per volume of etherification catalyst per hour.

Within the etherification reaction zone 10, methanol will exothermicallyreact with the tertiary butyl alcohol to form methyl tertiary butylether which will be contained in a reaction product discharged from theetherification reaction zone 10 by way of a line 20 leading to a firstmethyl tertiary butyl ether (MTBE) distillation zone 30.

As a specific example, when the solid etherification catalyst is asulfonic acid resin such as Amberlyst 15 and when the molar ratio ofmethanol to tertiary butyl alcohol in the feed mixture charged to theetherification reaction zone 10 by the line 14 is within the ratio ofabout 2.0 moles of methanol per mole of tertiary butyl alcohol, and thereaction is conducted at a temperature of about 110° C. at a feed rateof about 2.0 volumes of feed mixture per volume of catalyst per hour,the etherification reaction product may have the composition in partshown by the following table:

ETHERIFICATION REACTION PRODUCT

    ______________________________________                                                      wt. %                                                           Component     (Approx.)                                                       ______________________________________                                        Water         14.0                                                            Methanol      27.6                                                            Isobutylene    3.0                                                            TBA.sup.1     14.1                                                            MTBE.sup.2    34.5                                                            Other.sup.3    6.8                                                            ______________________________________                                         .sup.1 Tertiary butyl alcohol                                                 .sup.2 Methyl tertiary butyl ether                                            .sup.3 Includes the acetone, propanol, ditertiary butyl peroxide, tertiar     butyl formate, etc. initially present in the tertiary butyl alcohol           feedstock.                                                               

The etherification reaction product charged to the first MTBEdistillation zone 30 by way of the charge line 20 is fractionatedtherein under distillation conditions including a liquid refluxtemperature of about 30° to about 100° C., and more preferably about 40°to about 80° C., a reboiler temperature of about 80° to about 115° C.,and more preferably from about 95° to about 105° C., and a pressure ofabout 15 to about 60 psia, the distillation condition being selectedsuch that substantially all of the MTBE in the etherification reactionproduct 20 is taken overhead from the first distillation zone 30 by aline 32. As a consequence, the first distillation fraction 32 takenoverhead from the distillation zone 30 will comprise substantially allof the isobutylene and substantially all of the methyl tertiary butylether and some of the methanol charged to the first distillation zone30. The second heavier distillation fraction 34 discharged from thefirst MTBE distillation zone 30 will comprise methanol, tertiary butylalcohol and water.

In accordance with the present invention, the first distillationfraction 32 in admixture with recycle isobutylene added by a recycleline 89 is charged by way of manifold 33 and charge line 35 to anisobutylene conversion zone 40 containing a bed of solid resinetherification catalyst such as a bed of Amberlyst 15 sulfonatedpolystyrene-divinyl benzene copolymer acidic ion exchange resin.Suitably, the admixture in the line 35 will contain about 2 to about 15parts of recycle isobutylene per 100 parts of first distillationfraction 32.

Etherification reaction conditions established in the isobutyleneconversion zone 40 include, for example, a temperature of about 35° toabout 130° C., and more preferably from about 40° to about 70° C., apressure of about 50 to about 500 psia, and more preferably from about150 to about 250 psia, and a contact time of about 0.5 to about 4volumes of first distillation fraction per volume of solid resinetherification catalyst per hour. As a consequence, a portion of themethanol and isobutylene contained in the first distillation fraction 32will be converted to methyl tertiary butyl ether. Typically, theconversion will amount to about 30 to about 60 wt. %, based on theisobutylene.

As a consequence, there will be formed an isobutylene conversion productdischarged from the isobutylene conversion zone 40 by a line 42 leadingto a methanol solvent extraction zone 50. The composition of a typicalisobutylene conversion product may be characterized as follows:

ISOBUTYLENE CONVERSION PRODUCT

    ______________________________________                                                      wt. %                                                           Component     (Approx.)                                                       ______________________________________                                        Isobutylene   5.4                                                             MTBE          79.5                                                            Methanol      12.2                                                            Other         2.9                                                             ______________________________________                                    

In accordance with the present invention, the isobutylene conversionproduct 42 together with recycle isobutylene charged by a recycle line83 is charged through line 41 to a manifold 44 and thence via line 46 toa methanol solvent extraction zone 50 where it is counter-currentlycontacted with water introduced into the solvent extraction zone 50 by acharge line 52 controlled by a valve 54.

Within the methanol solvent extraction zone 50, solvent extractionconditions are established for countercurrent solvent extractionincluding a ratio of water to extraction feed mixture within the rangeof about 0.05 to about 0.3 parts of water per part of extraction feedmixture per hour, and more preferably a ratio of about 0.08 to about 0.2parts of water per part of extraction feed mixture. Extractiveconditions to be established may suitably include a temperature of about20° to about 60° C., and more preferably from about 30° to about 40° C.,and a pressure of about 50 to about 500 psia, and more preferably fromabout 50 to about 150 psia.

As a consequence, a supernatant raffinate will be formed which iswithdrawn from the methanol solvent extraction zone 50 by line 60. Theextract is discharged from the solvent extraction zone 50 by way of abottoms charge line 64 leading to a third methyl tertiary butyl etherdistillation zone 70.

Within the second methyl tertiary butyl ether purification distillationzone 62, distillation conditions are established including a liquidreflux temperature of about 30° to about 60° C., and more preferablyfrom about 40° to about 55° C., a reboiler temperature of about 100° toabout 140° C., and more preferably from about 125° to about 135° C. anda pressure of about 70 to about 120 psia, and more preferably from about90 to about 110 psia, to thereby form a lighter distillation fraction 66discharged from the second distillation zone 62 and a heavier fourthdistillation fraction 68 consisting essentially of product, namelymethyl tertiary butyl ether.

The third distillation fraction 66 will comprise a mixture ofisobutylene and water and suitably charged to a decantation zone 80where it can settle to form a supernatant isobutylene phase withdrawnfrom the decantation zone 80 by way of a line 82. Water is dischargedfrom the decantation zone 80 by way of a water discharge line 84 and issuitably purged from the system. A portion of the isobutylene in theline 82 is recycled by way of manifold 86, line 89 controlled by valve87, manifold 33 and line 34 to the isobutylene conversion reaction zone40 as a first isobutylene recycle fraction and another portion of theisobutylene in the line 82 is recycled to the methanol solventextraction zone 50 through a branch line 83 controlled by a valve 85 asa second isobutylene recycle fraction. Suitably, about 10 to about 15wt. % of the isobutylene in line 82 is discharged from manifold 86 asthe first isobutylene recycle fraction and about 90 to about 85 wt. % isdischarged as the second isobutylene recycle fraction.

The extract 64 charged to the third distillation zone 70 will comprisemethanol, water and residual quantities of methyl tertiary butyl etherand isobutylene, and is suitably fractionated therein under distillationconditions including a liquid reflux temperature of about 30° to about90° C., and more preferably from about 50° to about 75° C., and areboiler temperature of about 80° to about 120° C., and more preferablyfrom about 105° to about 115° C., and a pressure of about 15 to about 60psia, and more preferably from about 40 to about 50 psia, to form afifth lighter distillation fraction 72 comprising methyl tertiary butylether which may suitably be charged to the manifold 44 for the chargeline 46 to the methanol solvent extraction zone 50. A sixth heavierdistillation fraction comprising water and methanol is discharged fromthe third distillation zone 70 by a line 74 leading to a fourthdistillation zone 90. The sixth distillation fraction charged to thefourth methanol distillation zone 90 is fractionated therein underdistillation conditions which may suitably include a liquid refluxtemperature of about 30° to about 80° C., and more preferably from about60° to about 75° C., a reboiler temperature of about 100° to about 140°C., and more preferably from about 110° to about 120° C., and a pressureof about 15 to about 60 psia, and more preferably from about 20 to about30 psia, into a seventh lighter distillation fraction 92 which may besuitably charged to a manifold 93 and from thence by line 112 to themanifold 12 for recycle to the etherification reaction zone 10 throughfeed line 14. A heavier distillation fraction consisting essentially ofwater is discharged from the fourth methanol distillation zone by way ofa line 94 and may be discharged from the system through manifold 95 andwater discharge line 96.

The second distillation fraction 34 discharged from the first MTBEdistillation zone 30 in accordance with the present invention is chargedto a fifth tertiary butyl alcohol recovery distillation zone 100 whereit is fractionated under distillation conditions including a liquidreflux temperature of about 35° to about 170° C., and more preferablyabout 140° to about 150° C., and a reboiler temperature of about 100° toabout 190° C., more preferably about 170° to about 180° C., and at apressure of about 15 to about 190 psia, and more preferably about 110 toabout 160 psia, into a ninth distillation fraction discharged from thefifth distillation zone 100 by a line 102 leading to manifold 103 and atenth heavier distillation fraction comprising a third water fractiondischarged from the distillation zone 100 by a line 106 leading by wayof manifold 95 to the water discharge line 96.

In accordance with one embodiment of the present invention, the ninthdistillation fraction 102 is charged to a manifold 103 provided with adischarge line 118 controlled by a valve 116 leading to the feedmanifold 12 so that the methanol can be directly charged to theetherification reaction zone 10 from manifold 12 through feed line 14. Asecond branch line 120 controlled by a valve 98 is provided which leadsfrom manifold 103 to the feed manifold 44 for the methanol extractionzone 50 so that all or a portion of the ninth distillation fraction 102may be recycled to the manifold 44.

EMBODIMENT OF FIG. 2

Another embodiment is disclosed in FIG. 2.

Turning now to FIG. 2, it will be noted that the isobutylene dischargedfrom the decantation zone 80 by the line 82 is charged to a manifold 200from which a portion of the isobutylene is charged to the recycle line89 for processing as described above. Another portion of the isobutyleneis discharged from the manifold 200 by a branch line 202 controlled by avalve 204 leading to a surge tank 210, which will suitably be of acapacity adequate to hold an inventory of isobutylene sufficient toprovide for about 12 to 36 hours of continuous operation of the waterextraction zone 50.

In accordance with this embodiment of the present invention, the waterextraction zone 50 is suitably a counter-current extraction tower of thetype known to those skilled in the art. However, it is operated in amanner different from the manner described above. In accordance withthis embodiment, isobutylene is discharged from the surge drum 210 by aline 212 controlled by a valve 214 leading to a charge point below thepoint at which the isobutylene conversion product 46 is charged to thewater extraction zone 50; being preferably charged about 1 to about 3theoretical plates below the point of introduction of the isobutyleneconversion product 46 and about 0 to about 1 theoretical plates abovethe bottom of the water extraction zone 50 so as to selectively contactonly the extract.

Extraction conditions established in the extraction tower may suitablyinclude a temperature of about 20° to about 60° C., and more preferablyabout 30√ to about 40° C., a pressure of about 50 to about 500 psia andmore preferably about 50 to 150 psia, and a residence time of about 4hours to about 8 hours for the aqueous phase and from about 0.04 hour toabout 0.10 hour for the organic phase.

The water suitably may be charged by the line 52 to the extraction zone50 in the ratio of about 0.05 to about 0.3 part of water per part ofextraction feed charged to the extraction zone 50 by the line 46, andmore preferably in the ratio of about 0.08 to about 0.2 part of waterper part of extraction feed charged to the extraction zone 50.Isobutylene suitably may be charged by the line 212 to the extractionzone 50 in the ratio of about 0.3 to about 1 part of isobutylene perpart of methyl tertiary butyl ether in the extraction feed charged tothe extraction zone 50 by the line 46, and more preferably in the ratioof about 0.5 to about 0.7 part of isobutylene per part of methyltertiary butyl ether in the extraction feed charged to the extractionzone 50 by the line 46.

The raffinate 64 discharged from the methanol extraction zone 50 ischarged to the second MTBE distillation zone 62, which is operated inthe manner described above in order to provide a lighter fraction 66comprising a mixture of water and isobutylene and a heavier MTBE productfraction 68. The lighter fraction 66 is charged to the decantation zone80 wherein isobutylene is decanted and discharged by the line 82 forprocessing as described above and wherein the water is accumulated fordischarge by the line 84.

The extract fraction 64 discharged from the methanol extraction zone 50by the line 64 is processed in the manner described above.

OPERATION

In accordance with a preferred embodiment of the present invention, atertiary butyl alcohol feedstock is continuously charged to peroxidedecomposition zone 11 by a line 13 where it is thermally treated underthermal peroxide decomposition conditions including a temperature ofabout 100° to about 200° C., a pressure of about 80 to about 500 psiaand a flow rate of about 0.5 to 4 volumes of feedstock per reactorvolume per hour to thereby provide a substantially peroxides-freetertiary butyl alcohol reaction product.

The peroxides-contaminated feedstock and the substantiallyperoxides-free reaction product discharged from the peroxidedecomposition zone 11 will typically have compositions as follows:

PEROXIDE DECOMPOSITION ZONE FEED AND PRODUCT

    ______________________________________                                                       Approx.  Approx.                                                              Feed     Product                                               Component      (wt. %)  (wt. %)                                               ______________________________________                                        ATBP.sup.4     0.39     0.00                                                  DTBP.sup.1     0.87     0.02                                                  TBA.sup.2      97.2     97.4                                                  Water          0.1      0.02                                                  Other.sup.3    1.44     2.56                                                  ______________________________________                                         .sup.1 Ditertiary butyl peroxide                                              .sup.2 Tertiary butyl alcohol                                                 .sup.3 Includes acetone, tertiary butyl formate, isopropyl alcohol, etc.      .sup.4 Allyl tertiary butyl peroxide                                     

The substantially peroxides-free tertiary butyl reaction product 17 ischarged to the manifold 12 together with fresh methanol feedstock 15 andthe recycle fraction 112 in amounts, for example, such that the chargeratio of methanol to tertiary butyl alcohol in the feed line 14 amountsto about 2 moles of methanol per mole of tertiary butyl alcohol.

The feed mixture is discharged from the manifold 12 by a line 14 leadingto etherification reaction zone 10 containing a bed of a suitableetherification catalyst, such as Amberlyst 15 catalyst. Within theetherification reaction zone 10, the feedstock is passed through theetherification reaction bed on a continuous basis under reactionconditions, as described above, to thereby provide a reaction producthaving the following composition:

ETHERIFICATION REACTION ZONE 10 REACTION PRODUCT

    ______________________________________                                                      wt. %                                                           Component     (Approx.)                                                       ______________________________________                                        Methanol      27.6                                                            TBA           14.5                                                            Water         14.0                                                            Isobutylene    3.0                                                            MTBE          34.5                                                            Acetone        0.4                                                            2-Propanol     6.0                                                            ______________________________________                                    

The etherification zone reaction product is discharged from the reactionzone 10 by a line 20 leading to first methyl tertiary butyl etherdistillation zone 30 where the fraction 20 is separated into a firstlighter distillation fraction 32 comprising about 6.5 wt. % isobutylene,about 16.5 wt. % methanol, about 75 wt. % MTBE and about 2 wt. % othercomponents, and a second heavier fraction comprising about 37 wt. %methanol, about 26.0 wt. % tertiary butyl alcohol, about 25.5 wt. %water, 11 wt. % isopropanol and about 0.5 wt. % of other components.

The first distillation fraction 32 along with recycle isobutylene 89 iscontinuously charged to an isobutylene conversion zone 40 through theline 34 and brought into contact therein with a solid resinetherification catalyst, such as Amberlyst 15 catalyst, under conversionconditions, as described above, to thereby convert about 50 wt. % of theisobutylene and a portion of the methanol in the first distillationfraction to MTBE and to form an isobutylene conversion product which isdischarged from the isobutylene reaction zone 40 by a line 42 and whichtypically has the following composition:

ISOBUTYLENE CONVERSION FEED AND PRODUCT, wt. %

    ______________________________________                                                        Approx.  Approx.                                                              wt. %    wt. %                                                Component       Feed     Product                                              ______________________________________                                        Isobutylene     11       5.5                                                  MTBE            71       79.5                                                 Methanol        15       12                                                   Other            3       3                                                    ______________________________________                                    

The isobutylene conversion fraction 42 and the isobutylene recyclefraction 83 are continuously charged to the manifold 44 by a line 41leading from manifold 45. The isobutylene mixture is discharged from themanifold 44 together with recycle fraction 120 and recycle fraction 72by a feed line 46 leading to methanol extraction zone 50 in the ratio ofabout 2 parts of isobutylene conversion product per part of recycleisobutylene. Water is charged to the methanol extraction zone 50 by awater charge line 52 in an amount such that the ratio of water toisobutylene and isobutylene conversion product in the methanolextraction zone 50 is in the range of about 0.05 to about 0.3 parts ofwater per part of extraction zone feed mixture.

Within the methanol extraction zone, the methanol is extracted from theisobutylene conversion product under extraction conditions as describedabove to thereby provide an overhead raffinate fraction 60 comprisingisobutylene and methyl tertiary butyl ether and residual quantities ofwater and an extract 64 comprising methanol, water and residualquantities of isobutylene and methyl tertiary butyl ether.

The raffinate is fed by a line 60 to a second methyl tertiary butylether purification distillation zone 62 where it is resolved bydistillation into a third lighter distillation fraction 66 comprisingisobutylene and water and into a fourth heavier distillation fraction 68consisting essentially of methyl tertiary butyl ether which isdischarged as product.

The third distillation fraction 66 is charged to a decantationseparation zone 80 where it is permitted to settle and is resolved intoan isobutylene fraction 82 and a first water fraction 84 which isdischarged from the system.

The isobutylene fraction 82 is suitably recycled to the isobutyleneconversion zone 40 in admixture with the first distillation fraction 32and to the feed to the methanol extraction zone 50.

Typically, about 2 to about 10 parts of recycle isobutylene from theline 89 will be mixed with 100 parts of overhead product from the firstdistillation fraction 32.

The extract 64 is continuously charged to a third methyl tertiary butylether distillation zone 70 where it is separated into a lighter fifthdistillation fraction 72 comprising methyl tertiary butyl ether and asixth heavier distillation fraction 74 comprising methanol and water.The fraction 74 is continuously charged to a fourth methanoldistillation zone 90 wherein it is separated by fractional distillationinto a seventh lighter distillation fraction 92 comprising methanol andan eighth distillation fraction comprising water which is discharged bya line 94. In accordance with the preferred embodiment of the presentinvention, the fraction 92 together with fraction 118 is charged by aline 112 to feed manifold 12.

The second distillation fraction 34 from the first MTBE distillationzone 30 is continuously charged to a fifth tertiary butyl alcoholrecovery distillation zone 100 where it is separated into a ninthlighter distillation fraction 102 comprising methanol, tertiary butylalcohol and water and a tenth heavier distillation fraction 106comprising water. The tenth heavier distillation fraction is dischargedby a line 106 and the water in line 106, together with the water in line94, may suitably discharge from the system from manifold 95 throughwater discharge line 96.

EXAMPLES Example 1

As an example of the embodiment of the present invention, as illustratedin FIG. 1, the extraction column 50 consisting of 7 theoretical stagesmay be operated at a temperature of about 37° C. and a pressure of about155 psia. An extraction feedstock comprising a mixture of theisobutylene conversion product and recycled isobutylene is charged tothe bottom stage of extraction column 50 by the line 46 and water ischarged to the top stage by line 52 in the ratio of about 11 parts ofextraction feedstock per part of water. The composition of theextraction feedstock, the charge water, the raffinate and the extract isgiven in the following table.

Note from Table 1 the substantial absence of methanol in the raffinateand the substantial presence of MTBE in the extract.

                                      TABLE 1                                     __________________________________________________________________________    Solvent Extraction of Methanol from                                           Methanol-Contaminated Methyl Tertiary Butyl Ether                                    Extraction                                                                    Feed     Water    Extract Raffinate                                    Item   wt. %                                                                              Parts                                                                             wt. %                                                                              Parts                                                                             wt. %                                                                              Parts                                                                            wt. %                                                                             Parts                                    __________________________________________________________________________    Methanol                                                                             8.93  89 0.80 1   41.59                                                                              86 0.49                                                                               4                                       MTBE.sup.1                                                                           55.82                                                                              558 0    0   11.75                                                                              24 60.42                                                                             534                                      Water  0.10  1  99.20                                                                              99  41.00                                                                              84 0.64                                                                               6                                       IBTE.sup.2                                                                           31.60                                                                              316 0    0    2.63                                                                               5 35.14                                                                             311                                      Other  3.55  36 0    0    3.03                                                                               7 3.31                                                                               29                                      Total (Parts)                                                                             1000     100      206    884                                      __________________________________________________________________________     .sup.1 Methyl tertiary butyl ether                                            .sup.2 Isobutylene                                                       

                                      TABLE 2                                     __________________________________________________________________________    Solvent Extraction of Methanol from                                           Methanol-Contaminated Methyl Tertiary Butyl Ether                                    Extraction                     Recycle                                        Feedstock                                                                             Water   Extract                                                                              Raffinate                                                                             Isobutylene                             Item   wt. %                                                                             Parts                                                                             wt. %                                                                             Parts                                                                             wt. %                                                                             Parts                                                                            wt. %                                                                             Parts                                                                             wt. %                                                                             Parts                               __________________________________________________________________________    Methanol                                                                             12.37                                                                             124 0.80                                                                              1   45.74                                                                             122                                                                              0.53                                                                               7  1.01                                                                               4                                  MTBE.sup.1                                                                           79.38                                                                             794 0   0   0.33                                                                               1 61.71                                                                             800 1.54                                                                               7                                  Water  0.07                                                                               1  99.20                                                                             128 45.17                                                                             121                                                                              0.66                                                                               8  0.16                                                                               1                                  IBTE.sup.2                                                                           5.61                                                                               56 0   0   4.51                                                                               12                                                                              34.04                                                                             441 91.48                                                                             397                                 Other  2.57                                                                               25 0   0   4.25                                                                               11                                                                              3.06                                                                               40 5.81                                                                               25                                 Total (Parts)                                                                            1000    129     267    1296    434                                 __________________________________________________________________________     .sup.1 Methyl tertiary butyl ether                                            .sup.2 Isobutylene                                                            .sup.3 Also, about 308 parts of isobutylene were charged by line 212     

Example 2

As an example of the embodiment of the present invention, as illustratedin FIG. 2, the extraction column 50 consisting of 7 theoretical stagesmay again be operated at a temperature of about 37° C. and a pressure ofabout 155 psia. An extraction feedstock comprising the isobutyleneconversion product is charged to the extraction column 50 by the line46, recycle isobutylene is charged by the line 212 and water is chargedby line 54 to the top stage in the ratio of about 11 parts of extractionfeedstock plus recycle isobutylene per part of water. The recycleisobutylene is fed 2 theoretical stages below the extraction feedstock.The composition of the extraction feedstock, the charge water, theraffinate, the extract and the recycle isobutylene is given in thefollowing table.

Note from Table 2 not only the substantial absence of methanol in theraffinate but also the almost total absence of methyl tertiary butylether from the extract.

Example 3 Description of Pilot Plant Methanol Extraction Column

As an additional example of the present invention, as illustrated inFIG. 1, a pilot unit was operated for 6 days.

The MTBE pilot plant methanol extraction column consists of three, 5'flanged sections of 1.5", 316 stainless steel, schedule 40 pipe. Each ofthe three sections is packed with 1/4" ceramic raschig rings providing atotal of 15' of packing. Temperature control is maintained throughelectrical resistance heating coils wrapped around the outer surface ofthe column and extending over the entire length of the column. Feedtemperature control is maintained through electrical resistance heaterson both the aqueous and organic feed lines.

The column pressure is controlled through a pressure control valve onthe raffinate stream. The level of the interface between the organic andaqueous layers in the column is indicated through a differentialpressure transmitter and controlled by a level control valve on theextract line. The interface level can also be viewed in a sight glassattached to the column. The organic and aqueous flows to the column aremonitored through Coriolis type flow meters and are controlled throughflow control valves. Overall material balance is verified by digitalscales on the feed, raffinate, and extract tanks.

The column and all supporting equipment are connected to a digitalcontrol system which provides both data gathering and control.

    ______________________________________                                        Results from Pilot Plant Tests                                                           Feed  Water     Raffinate                                                                              Extract                                   ______________________________________                                        Methanol                                                                              wt. %    9.08    0.00    0.18   34.50                                         (parts)  (91)    (0)     (2)    (87)                                  MTBE    wt. %    56.55   0.00    60.18  10.38                                         (parts)  (566)   (0)     (548)  (26)                                  Water   wt. %    0.24    100.00  1.84   50.40                                         (parts)  (2)     (137)   (17)   (127)                                 IBTE    wt. %    33.37   0.00    37.23  4.13                                          (parts)  (334)   (0)     (339)  (10)                                  Other   wt. %    0.76    0.00    0.57   0.59                                          (parts)  (7)     (0)     (5)    (2)                                   Total Flow                                                                            (parts)  1000    137     911    252                                   ______________________________________                                    

Having thus described our invention, what is claimed is:
 1. A method forthe continuous purification of methyl tertiary butyl ether contaminatedwith isobutylene, methanol and water, which comprises:continuouslycharging an extraction feed comprising water isobutylene, methanol andmethyl tertiary butyl ether to a methanol extraction zone comprising acounter-current contact tower and countercurrently contacting saidextraction feed therein with water to provide an organic phase overheadraffinate comprising isobutylene, methyl tertiary butyl ether and aminor amount of water and a water phase extract comprising methanol,water and a minor amount of methyl tertiary butyl ether and strippingsaid extract with an isobutylene fraction in said extraction tower toremove most of said methyl tertiary butyl ether therefrom, continuouslycharging said raffinate to a methyl tertiary butyl ether purificationdistillation zone and separating said raffinate therein into a lighterdistillation fraction comprising isobutylene and water and a heavierdistillation fraction consisting essentially of methyl tertiary butylether; continuously charging said lighter distillation fraction to adecantation separation zone and separating it therein into a distillateisobutylene fraction and a water fraction; continuously accumulatingisobutylene from said distillate isobutylene fraction in a surge drumhaving a capacity adequate to provide for about 12 to 36 hours ofcontinuous operation of said counter-current contact tower, continuouslyreturning distillate isobutylene from said surge drum to saidcounter-current contact tower at a charge point about 1 to 3 theoreticalplates below the point of introduction of said extraction feed.
 2. Amethod as in claim 1 wherein the extraction conditions in the extractiontower include a temperature within the range of about 20° to about 60°C., a pressure of about 50 to about 500 psia and a residence time ofabout 4 to about 8 hours for the water phase and from about 0.04 toabout 0.10 hour for the organic phase.
 3. A method as in claim 2 whereina ratio of about 0.05 to about 0.3 parts of water per part of extractionfeed and a ratio of about 0.3 to about 1 part of isobutylene per part ofmethyl tertiary butyl ether in the extraction feed are maintained in theextraction tower.
 4. A method as in claim 1 wherein the extractionconditions in the extraction tower include a temperature within therange of about 30° to about 40° C., a pressure of about 50 to about 150psia and a residence time of about 5 to about 7 hours for the waterphase and from about 0.06 to about 0.08 hour for the organic phase.
 5. Amethod as in claim 4 wherein a ratio of about 0.08 to about 0.2 parts ofwater per part of extraction feed and a ratio of about 0.5 to about 0.7part of isobutylene per part of methyl tertiary butyl ether in theextraction feed are maintained in the extraction tower.